_Volcanic Mountains and Table-Lands._--In the south-central portion of the Great plateaus in southwestern Colorado and eastern New Mexico, there are several typical cinder cones with lava-flows associated with them, which impart novel topographic forms to the general monotony of the broad plateau surfaces. The highest of the extinct volcanoes in this region is Mount Capulin, situated in northeastern New Mexico, about 200 miles east of the Rocky Mountains, which rises 2,750 feet above the surrounding plain, and has an elevation of about 9,000 feet above the sea. At the summit of this conical mass there is a well-defined crater a mile in diameter. In the same region there are several other similar volcanic cones, from which lava streams have descended. As has been pointed out by R. T. Hill, these are the most easterly volcanoes of recent geological age in North America. They were formed after the Tertiary rocks of the Llano were laid down. The Raton Mesa, situated between Mount Capulin and the front range of the Rockies, is capped by a lava flow of more ancient date than the volcanoes just referred to, which has protected the softer rocks beneath from erosion, and now stands as a prominent table-land with precipitous borders. THE PACIFIC MOUNTAINS To the west of the Continental basin is a vast cordillera composed of numerous mountain chains which extends from south-central Mexico northward to the Arctic Ocean, and in its broadest part is about 1,000 miles wide. As already explained, we speak of this region in its entirety as the Pacific cordillera, or less technically as the Pacific mountains. It is a highly complex group of mountain chains, each of which contains two or more distinct mountain systems; each system, again, is usually composed of many ranges, and each range is frequently made up of a multitude of ridges, peaks, buttes, mesas, etc.; there are also many plateaus more or less completely dissected by erosion, and broad valleys, as well as numerous canyons, gulches, ravines, arroyas, and other secondary topographic forms. This vast cordillera not only contains mountains produced by the folding of the rocks of the earth's crust, in a general way similar to the Appalachians in structure, but also upturned blocks many miles in extent, bounded by breaks or faults, and volcanic mountains, vast lava-flows, and elevations due to the injection of molten rock into the earth's crusts so as to elevate domes. In fact, scarcely any topographic form and no important geological structure that is known is lacking in this great family of mountains which dominates the western portion of the continent.